The present invention relates to nacreous pigments having improved light fastness and which are based on mica flakes coated with metal oxides.
A basic requirement for these pigments, in particular as regards their outdoors use, is an adequate light and weathering fastness. A number of processes have already been proposed which are intended to improve the light fastness of such mica flakes which are usually coated with TiO.sub.2. Thus, German Offenlegungsschrift No. 2,106,613 proposes an additional treatment of the pigments with silicate after the actual coating of the mica with TiO.sub.2. In German Offenlegungsschrift No. 2,215,191 and German Offenlegungsschrift No. 2,852,585 external coatings of methacrylatochromium(III) chloride or of chromium hydroxide respectively are applied to obtain stability to light.
Nevertheless, there still exists a need for pigments which, on the one hand, have very good light fastness and, on the other hand, are also simpler to prepare than known pigments, which usually require an additional process step to achieve stability to light.